21. Which of the statements best describes the mutational event pictured below?
Wild-type sequence ACC   CAC   UCU   GGA   UUU   AAG   GCA
 Peptideencoded   thr   his   ser   gly   leu   lys   ala Mutant sequence ACC   CAC   UCU   UGA   UUU   AAG   GCA
Peptideencoded   thr   his   ser   stop   phe   lys   ala
(A) A transversion mutation leading to a nonsense codon
(B) A frameshift mutation leading to a missense amino acid substitution
(C) A transition mutation resulting in a silent amino acid substitution
(D) A transition mutation leading to a nonsense codon
(E) An insertion mutation resulting in a frameshift of the amino acid sequence